(1) Field of the Invention
This invention relates to lighting circuits and, more particularly, to LED lighting circuits including conductors and heat sinks molded of conductive loaded resin-based materials comprising micron conductive powders, micron conductive fibers, or a combination thereof, homogenized within a base resin when molded.
(2) Description of the Prior Art
Lighting sources are used in a large variety of applications to provide indication and illumination. Lighting indication, or indicator lighting, is light used to deliver a message. Indicator lighting is widely used in signs, streetlights, automobiles, appliances, machinery, computers, entertainment devices, electronics, and the like. Automobile brake lights and computer ‘ON’ LED lights are examples of indicator lighting. Lighting illumination, or illuminating lighting, is used to provide, or to enhance, lighting for human activity. Illumination lighting is widely used in homes, offices, factories, schools, institutions, automobiles, and the like. Automobile headlights and office fluorescent lighting are examples illumination lighting.
Most modern lighting sources are powered by electricity. Electrically powered lights may be generally categorized as incandescent, gas/fluorescent, and solid state. Incandescent lights, such as common light bulbs, rely on an incandescing filament, such as tungsten wire, to generate light. Unfortunately, much of the electrically energy is converted into infrared radiation (heat) that is not detectable to the unaided human eye. Gas/fluorescent lights, such as neon lights, mercury vapor lamps, halogens lamps, and the like, rely on gas discharge phenomenon to generate light. Fluorescent bulbs can be substantially more efficient than incandescent bulbs in converting electrical energy into useful light energy. However, fluorescent bulbs may require relatively sophisticates starter and ballast circuits and frequently contain poisonous mercury.
Solid state lights, such as light emitting diodes (LED's), rely on the emission of photons (light energy) produced as electrons drop from conduction energy bands to lower orbital bands. Diodes are formed by bringing two slightly different materials together to form a PN junction. Typical PN junctions are formed from a semiconductor material such as silicon or aluminim-gallium-arsenide (AlGaAs) or the like. Pure, crystalline forms of these materials are poor conductors. However, the introduction of selected doping ions will make these materials conductive by creating extra electrons (n-type) or extra holes (p-type). When an n-type and a p-type material are put together, a PN junction, or PN diode is formed.
Under non-breakdown conditions, current (electrons) only flows in one direction in the diode—from N to P—under a positive voltage from P to N. The positive voltage provides energy for free electrons in the N region to jump from a lower orbital into a conduction orbital. These electrons then are able to move from the N region, across a central depletion region, and into the P region. Once in the P region, the electrons fall into empty hole locations and, as a result, drop from the conduction band into a lower orbital. This orbital drop results in the emission of a photon. All diodes release photon energy, however, only those which release energy in the spectrum of visible light are commonly called light emitting. To achieve a visible light photon emission, the energy gap between the conduction band and the lower orbitals must be wide. The width of this energy gap determines the wavelength of the photon and, therefore, the color of the emitted light.
LED devices convert part of the input electrical energy into visible light and part of this electrical energy into heat. The diode device is typically housed in a plastic lens. The photons emitted by the diode are omni-directional. However, the lens concentrates the light, using reflection, such that the light emitted from the top of the lens is substantially unidirectional and intense. LED devices are far more efficient than incandescent lights and more versatile than gas/fluorescent lights. LED devices generate little heat, though the heat that is generated is an important consideration in LED applications as will be described below. LED devices are in widespread use for indicators due to their low power consumption and multitude of colors. However, recent price reductions in semiconductor devices and the development of high intensity LED devices producing “white” light have resulted in more frequent use of LED devices for illumination applications. High intensity LED devices are now used as single lights, in applications such as flashlights, and as rows or arrays of lights, in applications such as taillights, traffic lights, flood lights, and signs.
Though LED devices are relatively simple, two terminal semiconductor devices, there are several considerations in designing and manufacturing LED lighting circuits. First, beyond the turn-ON voltage, the current response of the diode is exponential. Therefore, to prevent over-current damage to the diode, resistance must be placed in the circuit path. Typically, the resistance is placed in the path between the power supply and the anode (+) connection to the P side of the device while the cathode (−) connection to the N side is connected to ground. This resistance value is typically implemented as a discrete resistor that is either inserted or surface mounted onto the LED circuit board.
Second, although the LED generates less heat than an incandescent light, the heat that is generated in the junction is significant for several reasons. First, the performance of the LED is closely related to the junction temperature (Tjunction) of the device. It is found that the wavelength, or color, of light emitted from the LED varies with Tjunction. Therefore, a diode that is specifically designed for a color application, such as in a video array, may perform inaccurately at increased temperatures. It is found that the intensity (lumens) of light generated by an LED decreases with increasing temperature. This is especially significant since it may be tempting for the circuit designer or operator to increase current to maintain output intensity in an LED that is lagging due to high Tjunction. This can be counter productive and even result in damaging the LED since further increases in current also increase Tjunction. Unlike incandescent bulbs, LED devices do not have a distinctive wear-out mechanism to compare to filament breakage. Rather, it is found that the light intensity output of the device simply decreases over time. It is further found that high temperature operation shortens the time needed for degradation to occur. Based on all of the above observations, it is found that heat removal mechanisms, such as heat sinks, are very useful and/or necessary parts of LED-based lighting devices and, especially, those lighting devices using high output LED devices for illumination applications. However, in the prior art, heat sink structures typically comprise discrete, metal structures that must be manufactured and placed onto the LED circuit board. Further, resistors in LED lighting circuits are typically discrete devices that are mechanically placed on the lighting circuit. Each of these prior art approaches is found to increase the part count, the tooling costs, the assembly complexity, and the manufacturing costs of LED lighting systems.
Several prior art inventions relate to alternative electrical conductors and lighting systems. U.S. Pat. No. 5,685,632 Schaller, et al provides a light source such as battery-powered flashlights and lanterns, taillight assemblies of automobiles or motorcycles, battery housings, or head assemblies for light sources are formed from electrically conductive plastic. U.S. Pat. No. 5,771,027 to Marks, et al describes a composite antenna with a grid comprised of electrical conductors woven into the warp of a resin reinforced cloth forming one layer of the multi-layer laminate structure of the antenna. U.S. Pat. No. 6,249,261 Solberg, Jr., et al details a direction-finding antenna constructed from polymer composite materials that are electrically conductive. The polymer composite materials replace traditional metal materials. U.S. Pat. No. 6,138,348 Kulesza, et al presents a method for forming a bumped substrate and an electrical circuit that includes the bumped substrate. The method of forming the bumped substrate includes forming at least one electrically conductive polymer bump on each of a first set of bond pads of the substrate. At least one electrically conductive polymer bump is then formed on each of a second set of the bond pads of the substrate. U.S. Pat. No. 4,841,099 Epstein et al teaches an electrical component made from an electrically insulating polymer matrix filled with electrically insulating fibrous filler which is capable of heat conversion to electrically conducting fibrous filler and has at least one continuous electrically conductive path formed in the matrix by the in situ heat conversion of the electrically insulating fibrous filler.
Nv Bekaert sa of Kortrijk, Belgium is a manufacturer of metal yarns, knitted metal fabric, chopped metal fibers and pellets, and sintered porous media. The fibers are marketed with diameters of from 1 mm to 20 mm and may be chopped into fiber pieces or be of continuous yarns. The metals shown in the product description found www.bekaert.com Jan. 25, 2003 are stainless steel, temperature resistant alloys, nickel and nickel alloys, titanium, aluminum, and copper. “Fundamental Understanding of Conductivity Establishment for Electrically Conductive Adhesives,” Fan et al., Proceedings of the 52nd Electronic Components and Technology Conference, 2002, pp: 1154-1157, describes several epoxy resin based curing systems that were used as the matrices for isotropically conductive adhesives (ICAs). The ICAs exhibited different curing peak temperatures. This enables the investigation of the effects of the curing process upon the resultant bulk resistivity of the ICAs. The experimental results indicated a strong correlation between bulk resistivity and curing temperature or curing kinetics. “Advanced Packaging and Substrate Technology Using Conductive Adhesives,” Eda, Proceedings of 3rd International Conference on Adhesive Joining and Coating Technology in Electronics Manufacturing, 1998. pp: 144-151, discusses packaging and substrate technologies using conductive adhesives, stud bump bonding (SBB) and ALIVH (any layer inner via hole) high density wiring board. “Design And Understanding of Anisotropic Conductive Films (Acfs) for LCD Packaging,” Yim, et al., The First IEEE International Symposium on Polymeric Electronics Packaging, 1997, pp: 233-242, describes anisotropic conductive films (ACF) composed of an adhesive resin and fine conductive fillers such as metallic particles or metal-coated polymer balls. These resins and fillers are key materials for fine pitch chip-on-film (COF) and chip-on-glass (COG) LCD packaging. “Nanocomposite Materials Offer Higher Conductivity and Flexibility”, McCluskey, et al., Proceedings of 3rd International Conference on Adhesive Joining and Coating Technology in Electronics Manufacturing, 1998, pp: 282-286, describes the mechanical and electrical characteristics of a conductive polymer made with conductive silver flake nanoparticle fillers. The use of nanoparticle fillers allows the material to attain the same level of conductivity exhibited by traditional filled polymers at significantly lower particle loading. The conductive polymer combines the high conductivity and stability of a filled polymer with the flexibility and low density of an intrinsically conductive polymer.